Water resistance, density, and durability of biomass fuels

ABSTRACT

Given the current world situation of fuel shortages and conflict over the finite amount of fuels available, it is very prudent to utilize every avenue available to increase the amount and quality of fuels available to use in power generation as well as other applications of steam. There are hundreds of thousands of tons of natural fuels, available for use here as well as other parts of the world. The BTU value of these waste materials is immeasurable. While most of these alternative fuels do not contain the highest BTU value, the amount of them available is beyond belief. The biggest drawback to alternative fuels has been the ease of utilization and quality of the product introduced into the combustors. Many years of testing and research by this individual have resulted in a variety of fuels that in addition to adding to the fuel supply of the world&#39;s consumers, will help to clean up the emission problems that are coming to the forefront of environmental concerns.

BACKGROUND OF THE INVENTION

Biomass fuel proponents have struggled to find ways to maximize density,uniformity, and moisture-resistance of biomass fuel.

Most biomass fuels lack the density or uniformity that traditionalcombustors are fit to utilize, making them commercially unworkable.

Another major problems facing biomass fuel users is that the biomassfuel cubes or pellets are not resistant to water or moisture. Cubes orpellets begin to lose their integrity almost instantly when exposed tomoisture, rain, dew, or in some cases high humidity. This breakdownnecessitates covered storage and transport facilities and specialhandling, thereby increasing the cost of biomass fuel cube utilization.

BRIEF SUMMARY OF THE INVENTION

By blending biomass fuels with coal fines prior to their introductioninto a densification machine, the resulting product will be resistant towater damage.

In addition, using a blend of biomass and coal fines in biomass fuelproduction results in a product that has an increased density anddurability when compared to biomass fuels which do not contain coalfines. This increased density and durability is very important for theeconomics of transportation, handling, and the introduction of thebiomass fuel into a combustion system.

The foregoing and other objectives, features, and advantages of theinvention will be more readily understood upon consideration of thefollowing detailed description of the invention taken in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating the process of one embodimentof the process.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

By carefully blending biomass fuels with coal fines prior to theirintroduction into a densification machine, the resulting biomass fuelproduct is resistant to water damage. In some cases, depending on thepercentage of coal fines utilized, it is possible to obtain a resultingbiomass fuel which is almost totally waterproof.

By using a blend of biomass and coal fines in biomass fuel production,the density and durability of the biomass fuel product is increased ascompared to biomass fuel products which do not contain coal fines. It isbelieved that this increased density and durability is very importantfor the economics of transportation, handling, and the introduction ofthe fuel cube into a combustion system.

Mechanical processes for making biomass fuels are well known. Thebiomass material may be grass, grain, paper, animal wastes, wood waste,sewer sludge or other naturally occurring biological waste. Amanufacturer may pass this biomass material through one of a variety ofknown densification machines such as a cuber, pellet mill, briquettor,or extruder, to result in a biomass fuel product which is a cube,pellet, briquette, tablets, or similarly small structured smallparticles. Known densification machines may result in a product which issized for a particular combustion system.

The object of this invention is to produce a fuel which is a biomass andcoal combination and which is an improvement over non-coal containingbiomass fuels as it will have greater weight, improved water resistance,increased density, and greater durability.

The fuel combination may be manufactured by the following steps:

1. sizing of the biomass: solids in the biomass are sized to smallparticles.

2. adjusting the moisture content of the biomass: by drying or addingdesiccants, to reach a moisture content most appropriate for thedensifier.

3. adding coal fines: the ratio of coal to biomass by mass may varyaccording to the needs of the user. Higher coal content may result indiminished durability of the biomass fuel.

4. Re-adjusting the moisture content of the biomass and coal combinationif necessary for the densifier.

5. passing the biomass and coal combination through the densifier.

Some embodiments of the process described herein utilize biomassmaterial of various sources, of various moisture contents, and ofvarious sizes, which is mixed with coal fines in a variety of ratios,and then densified at various pressures. These embodiments aresummarized in the table below. The ranges given accommodate the factthat every seam of coal has its own characteristics with respect to itsactual hardness or grind, and volatile organic compound levels. BiomassMoisture content Biomass Coal Fine Percentage Coal fuel by weight SizeSize of coal fines Moisture Pressure Straw-type 5-25% 1 inch ¼ inch5-75% 5-25% 200-15,000 psi minus minus Sewer sludge, 5-25% No pre- ¼inch 5-75% 5-25% 200-15,000 psi paper, animal sizing minus wastenecessary Wood waste 5-25% ½ inch ¼ inch 5-75% 5-25% 200-15,000 psiminus minus

Biomass material may be delivered to a manufacturer with a variety ofmoisture content, ranging in biomass material which is dry to that whichis in liquid suspension or sludge. A manufacturer may have to adjust themoisture content of a biomass material either by adding moisture ordrying it, usually to a moisture range of 5-25% depending on the type ofdensifier and size of die to be used).

In addition, biomass material needs to be sized to pass through thevarious dies and agglomerate correctly. All of the bio-solids must bethoroughly mixed with the coal fines to ease the densification processby avoiding slugs of pure coal fines that can plug the machine, and toachieve a better quality final product. In the case of paper, 1½ inchminus, wood waste ½ inch minus or shavings, biological sludges do nothave to be mechanically sized prior to blending. Straw and grassesshould be sized to 1 inch minus.

The die temperature will increase if the manufacturer lowers the amountof moisture added just prior to entering the densifier. As the dietemperature increases so does the quality, durability, and waterresistance of the finished product.

The coal fine will be in the 1/4 inch minus range.

The amount of coal fines utilized (expressed by percentage of the totalweight) can range from 5% to 75% of the total weight. Above 75% of coalfines by weight, there is difficulty in maintaining cube or pelletintegrity resulting in a high percentage of “fines” in the finishedproduct.

In another embodiment of the process, the moisture resistance of thebiomass fuel product is increased by increasing the percentage of coalfines used in the process.

In another embodiment of the process, the durability and density of thebiomass fuel product is increased by increasing the friction, that isincreasing the amount of pressure used to pass the material through thedie. Additionally, durability and density can be increased by increasingthe die temperatures from ambient temperatures to 300 degreesFahrenheit. In another embodiment of the process, the ease of handlingbiomass fuel material in the densification process is increased by thepresence/absence of coal fines. When the material is passed through thedensifiers mentioned above, the bulk density of the material is greatlyincreased, allowing for easier handling and transportation withsignificantly lower amounts of fines generated by handling. In certaintypes of combustors, these fines cause a serious problem by not burningin the heat zone and by becoming a fly ash material that plugseconomizers and mulitclones, and overworks the electrostaticprecipitators.

Another embodiment is the creation of a biomass fuel product which ischaracterized by a zone which is resistant to or impervious to moisture.This zone is formed by passing a combination of biomass fuel materialand coal fines through a densification machine, such that oils in thecoal fines migrate to the exterior surface of the biomass fuel product.This zone can sometimes be seen when the biomass fuel product is broken,where it will appear as a fine line around the perimeter of the surfaceof the break.

Another embodiment of the process is the creation of a biomass fuelproduct which is lower in mercury, lead, cadmium, sulfur, and otherharmful metals than other non-biomass fuels, by blending biomass fuelmaterial with coal fines. This biomass fuel product, when combusted,will lower the emission of harmful metals as compared to combustion ofother coal fuel.

The terms and expressions which have been employed in the forgoingspecification are used therein as terms of description and not oflimitation, and there is no intention in the use of such terms andexpressions of excluding equivalence of the features shown and describedor portions thereof, it being recognized that the scope of the inventionis defined and limited only by the claims which follow.

1. A process for forming a combustible fuel from biomass materialcomprising the steps of: (a) adjusting a moisture content of a biomassmaterial; (b) adding coal fines to the biomass material to form amixture; and (c) compressing the mixture to form a biomass fuel.
 2. Theprocess of claim 1 additionally comprising the step of sizing thebiomass material.
 3. The process of claim 1 additionally comprising thestep of adjusting the moisture content of the mixture.
 4. The process ofclaim 1 wherein the moisture content of the biomass material is adjustedto the range of 5 to 25%.
 5. The process of claim 1 wherein the coalfines are a percentage 5 to 75% of the total weight of the mixture. 6.The process of claim 1 where the compression of the mixture is at 200psito 15,000psi and temperatures ranging from ambient to 300 degreesFahrenheit (pressure/temperature)